The patient typically has to manually make one or more of the connections of a fluid guide system, an example of which is disclosed in U.S. Pat. No. 6,368,314 B1 which is hereby incorporated into by reference, with a risk that the connection is not properly made. In daily use it may be possible for one of these connections to be broken without the patient noticing. In addition, flexing of the fluid guide system can cause breakages in the tube, or the tube could be punctured, and in either case this could happen without being noticed by the patient. A leakage in the flow path that is not noticed by the patient or detected by the pumping system will result in an under-delivery of drug. Occlusion can occur when there is a blockage in the flow path. This may arise from for example by kinking of the tube. An occlusion results in an under-delivery of drug and then a subsequent bolus being given when the blockage is removed.
Free-flow prevention is important to ensure that over-delivery of the drug cannot occur. Free-flow can arise from a pressure difference between the atmosphere and the interior of the pump housing. This may occur due to a sudden drop in atmospheric pressure, for example from flying in a plane or going up a mountain in a cable car. A high pressure pushing on a piston (in the following called “displacement member”) in the container that stores the drug will cause the piston to move forward and deliver drug into the patient which may be undesirable at that instant.
There are no methods for leakage detection in the flow path downstream of the adapter between the pump unit and the fluid guide system currently employed in infusion systems according to the present disclosure. The term of flow path within the framework of this application encompasses all parts of the injection device which function as a guidance of the fluid, for example adapters and valves, tubes of any kind, infusion sets and catheters which are used for guiding the fluid and any kind of fluid containers. Current methods for free-flow prevention include: Employing a sufficient friction of the displacement member in the container to prevent accidental movement of the displacement member, realizing a direct connection between the displacement member and a driven member which moves the displacement member, or inserting a valve into an adapter that links the container to the fluid guide system. In the following, the term “downstream” shall describe the direction of flow of the fluid to be administered which points towards the patient side end of the infusion system, i.e. towards the end of the catheter is inserted into the human and/or animal body. In contrast, the term “upstream” shall in the following denote the flow direction of the fluid to be administered which points in the direction the container.
Current methods for occlusion detection involve measuring the pressure in the flow path through the resultant force acting on the driven member that pushes against the displacement member. A force sensor is mounted behind the driven member and detects this force. For details about such a force sensor, it is referred to U.S. Pat. No. 6,368,314 B1. Alternative methods involve measuring the current through the drive motor.
It is desirable to have a means of pressure testing and free-flow prevention which allows for testing the pressure in and prevents free-flow from as many parts of the device. It therefore is preferable to have a control valve that is operable for pressure testing and is situated as far downstream as possible, in the best case just before the catheter tip that is inserted into the human and/or animal body. A control unit may further enable operation of the control valve and run a method for pressure testing before each administration of fluid in order to prevent administering a wrong dose to the organism.